1. Technical Field
The present invention relates to microelectronic devices in general, and in particular to a single-electron transistor for detecting biological molecules.
2. Description of the Related Art
Single-electron Transistor (SET) devices and fabrication methods are being widely investigated for high density and/or high performance microelectronic devices. As is well known to those having skill in the art, single-electron transistors use single-electron nanoelectronics that can operate based on the flow of single-electrons through nanometer-sized particles, also referred to as nanoparticles, nanoclusters or quantum dots. Although a single-electron transistor can be similar in general principle to a conventional Field Effect Transistor (FET), such as a conventional Metal Oxide Semiconductor FET (MOSFET), in a single-electron transistor, transfer of electrons may take place based on the tunneling of single-electrons through the nanoparticles. Single-electron transistors are described, for example, in U.S. Pat. Nos. 5,420,746; 5,646,420; 5,844,834; 6,057,556 and 6,159,620, and in publications by the present inventor Brousseau, III et al., entitled pH-Gated Single-Electron Tunneling in Chemically Modified Gold Nanoclusters, Journal of the American Chemical Society, Vol. 120, No. 30, 1998, pp. 7645–7646, and by Feldheim et al., entitled Self-Assembly of Single Electron Transistors and Related Devices, Chemical Society Reviews, Vol. 27, 1998, pp. 1–12, and in a publication by Klein et al., entitled A Single-Electron Transistor Made From a Cadmium Selenide Nanocrystal, Nature, 1997, pp. 699–701, the disclosures of which are hereby incorporated herein by reference in their entirety as if set forth fully herein.
A major breakthrough in single-electron transistor technology is described in U.S. patent application Ser. No. 09/376,695, entitled Sensing Devices Using Chemically-Gated Single Electron Transistors, by Daniel L. Feldheim and Louis C. Brousseau, III, also published as International Publication No. WO 01/13432 A1, the disclosures of which are hereby incorporated herein by reference in their entirety as if set forth fully herein. Described therein is a chemically-gated single-electron transistor that can be adapted for use as a chemical or biological sensor. Embodiments of these chemically-gated single-electron transistors include source and drain electrodes on a substrate and a nanoparticle between the source and drain electrodes, that has a spatial dimension of a magnitude of approximately 12 nm or less. An analyte-specific binding agent is disposed on a surface of the nanoparticle. A binding event occurring between a target analyte and the binding agent causes a detectable change in the characteristics of the single-electron transistor.
Notwithstanding these and other configurations of signle-electron transistors, including chemically-gated single-electron transistors, it may be difficult to fabricate these devices using conventional photolithography that is employed to fabricate microelectronic devices. In particular, in order to provide quantum mechanical effects with nanoparticles, it may be desirable to provide spacing between the source and drain electrodes of a single-electron transistor that is less than about 20 nm, or less than about 12 nm or about 10 nm. It may be difficult, however, to provide these spacings using conventional lithography at low cost and/or with acceptable device yields.